Stumble at idle, lost gas mileage, black soot in tail pipe

[zgeezer]

My wife's driver is a 2004 PTCruiser with the 2.4L High Output Turbo. We have 59,000 miles on it. Through 55,000 it got a steady 24+ mpg at our cruise control speeds to Nevada and Utah. Very clean exhaust pipe...No deposit on the interior of muffler tip. Does not consume any noticeable amount of oil. Less than 1/4 quart between oil changes at every 3,000. Two months ago, the car began to stumble at idle. At first, it would miss a beat every few days. Now every time we stop at a sign it drops a cylinder every few seconds. The tach just slowly swings between 500 and 760 rpm. The mileage on long trips with cruise control has dropped to 21+ and, sometimes down to 20mpg at steady speeds. The exhaust pipe now has a heavy deposit of black soot. A lot of it and it is not oily. Last month we dropped it off at our dealer for the 60,000 service and repair of problem. Vehicle returned to us with no change. The tech replaced plugs, did whatever else they do at 60,000 miles and assured me that the car "checks out good" and the a/f ratio is right on the money. No change. Still stumbles and consumes far more gas than it did 6 months ago. No CELs have been thrown. To me, the black dry soot in the tail pipe screams that it is running rich. The dealership tells me again that it "checks out" and that black soot deposits in the tail pipe are normal wear and tear and don't worry about it.

 

Am I just being picky or should I start replacing sensors, beginning the the O2 sensor.

 

Thanks for any comments.

 

g

[Kennysgreen280zt]

you might search over on http://www.srtforums.com the srt4 uses the same motor as the pt turbo and they have a large number of members over there. some of them are even mildly intelligent.

[zgeezer]

This site spoils you.

[A. G. Olphart]

As you have noted, the car has a problem... sounds like the dealership doesn't want to deal with it (under warranty). They may hope to ding you for bigger bucks later.

 

Black soot in the tailpipe of a modern vehicle is by no means normal; the catalytic converter is there to burn any leftover hydrocarbons, which it isn't doing. Converters sometimes plug up; if yours isn't plugged (just not getting hot enough to fire off???) it soon may be.

 

Since the vehicle is not using any more oil than usual, I'd say you're right about it running rich. As a guess, the oxygen sensor is no longer telling the computer the absolute truth. If it keeps screaming LEAN-LEAN-LEAN, the computer will tell the injectors MORE-MORE-MORE. The turbo throws in a bunch more variables that I'm even less qualified to assess.

 

You need a good honest tech.

 

.02 worth from a guy who has never had a car with a turbo, a computer, or a catalytic converter.

 

 

<>

[endurorider]

Your getting a missfire at idle. Did the tech look at the misfire counter? There is a monitor the tech can look at on his DRB (Chryslers) scan tool and see how many misfires occured on each of the four cylinders. I am suspecting a bad ignition coil. Another thing techs go by is looking at the long term fuel trim. 0% to 6% is acceptable. I perfer closer to 0%. the bigger the number the more fuel added the number goes neg fuel is taken away. If you want to throw parts, you have two coils if I remember right. It a waste spark system. Coils are pretty common on most newer cars to cause misfires. Injectors are a lot more rare. Usually in high mileage cars you'll see plugged or bad coils in them . coil should run you about 40-90 each. I don't think an occasional misfire would cause black soot exhaust pipe or poor mileage. If you had a o2 sensor on its way out causing a rich condition , I would think it would throw a code and the mil would be on. If it was me I would go back to the dealer and get with the service manger. One of the most important things to them is CSI . The survrey you get on the phone or the mail effects there bonus and what cars they get to sell. If you go to the service manger and you show your very upset and you want it fixed, they will turn your (heat) car over to a shop foreman Master tech instead of a lube tech who probleby did the service and has little experence.

[VinhZXT]

This problem could be caused by a bad cooland temp sensor. Does the newer cars throw any code when the coolant temp sensor goes bad? I gotta try this out on my C5 motor and let you know tonight. If the O2 sensor goes bad it will throw a code.

[zgeezer]

Thanks to everyone. I think I'll go back to the dealer and walk the service manager around this car and ask him if he can count the misfires and it sits there on idle.

 

g